Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$221.32	3.157%	$228.3071	$228.31	$228.30	$228.30
Purchase #2	$49.88	4.857%	$52.3027	$52.30	$52.30	$52.30
Purchase #3	$88.46	10.244%	$97.5218	$97.52	$97.50	$97.50
Purchase #4	$182.78	11.310%	$203.4524	$203.45	$203.45	$203.50
Purchase #5	$135.31	12.533%	$152.2684	$152.27	$152.25	$152.30
Purchase #6	$50.92	3.195%	$52.5469	$52.55	$52.55	$52.50
Purchase #7	$86.46	6.597%	$92.1638	$92.16	$92.15	$92.20
7 purchase totals =	$815.13		$878.5631	$878.56	$878.50	$878.60